1. Field of the Invention
The present invention relates to a conductive ceramic material and a production method thereof.
2. Description of the Related Art
In recent years, it has been reported that the step of pressure-molding powder of 12CaO.7Al2O3 (hereinafter, written as C12A7) as an oxide having a cage-like crystal structure, and thereafter holding and melting the molded powder at approximately 1600° C. in a reduction atmosphere, followed by annealing and coagulation, is repeated two times, or glass molten in the reduction atmosphere is crystallized in a vacuum atmosphere, whereby C12A7 polycrystal having conductivity of 5 S/cm can be produced (refer to Kim et al., J. Am. Chem. Soc., Vol. 127, pp. 1370-1371 (2005), and Kim et al., Chem. Mater., Vol. 18, pp. 1938-1944 (2006)). Moreover, it has been reported that a dry nitrogen atmosphere is used in the case of melting, annealing and coagulating the molded oxide powder, whereby C12A7 polycrystal having conductivity of approximately 100 S/cm can be produced only by performing the above-described step one time (refer to Japanese Patent Laid-Open Publication No. 2008-7374).
However, in accordance with such production methods as described above, the conductivity of the C12A7 polycrystal at room temperature is not higher than approximately 100 S/cm, which is insufficient. It can be expected that C12A7 polycrystal having sufficient conductivity will be used as a reducer. Moreover, since materials of the C12A7 polycrystal are composed of elements with large Clarke numbers, the C12A7 polycrystal can also be expected as an inexpensive conductive material. Furthermore, it can also be expected that the C12A7 polycrystal will be applied as a field emission electron emitter. Still further, it can also be expected that the C12A7 polycrystal will be applied as an electrode material of an electrochemical device accompanied with oxidation-reduction, and as an electrode for which special joint characteristics are required, such as a charge injection material in an organic EL device. From the above, as a subject, it is eagerly desired to provide the C12A7 polycrystal having the sufficient conductivity.
The present invention has been made in order to achieve the above-described subject. It is an object of the present invention to provide a conductive ceramic material having high conductivity.
It is another object of the present invention to provide a production method of a conductive ceramic material, which is capable of producing the 12CaO.7Al2O3 polycrystal having the high conductivity.